Concentric type electrode



w. J. SCOTT CONCENTRIC TYPE ELECTRODE Nqv. 12, 1957 2 Sheets-Sheet 1 Filed Nov. 223-1951 Inventor. 2 William J. 590th,

H is Att 01-11623 Nov. 12, 1957 w. J. SCOTT .CONCENTRIC- TYPE ELECTRODE 2 SheetsS heet 2 Filed Nov. 29, 1951,

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IhQentor: William J. Scott w/49% H is AttofTWe g.

CONCENTRIC TYPE ELECTRODE William J. Scott, Rugby, England, assignor to General Electric Company, a corporation of New York Application November 29, 1951, Serial No. 258,351

Claims priority, application Great Britain December 12, 1950 10 Claims. (Cl. 315-58) The present invention relates to an improved concentric type electrode and particularly to an improved electrode structure for use as a keep-alive electrode in a high frequency gaseous discharge device.

The present invention is particularly applicable to electric discharge apparatus embodying gaps cooperating with resonant openings or slots and adapted for use in microwave apparatus, where it is desired to alter the electrical characteristics of the gap by causing a discharge to take place across it. The gap then acts as a variable attenuator. Transmit-receive (T-R) and anti-transmitreceive (A. T. R.) devices are examples of such electronic discharge apparatus. A suitable filling for devices of this character includes a rare gas, such as argon, at a pressure of 8 to 12 millimeters of mercury at room temperature, together with water-vapor at a pressure up to 4 /2 millimeters of mercury.

In discharge devices of this type, it is generally desirable to maintain a discharge in the neighborhood of the main gap, defined by the two main electrodes, which is to be rendered conducting by a discharge under predetermined conditions, such as high frequency voltage conditions across the gap. This is often accomplished by means of a keep-alive or ignition electrode which is disposed in such relation to one main electrode so that a constant potential connected between the keep-alive electrode and the main electrode maintains a glow discharge therebetween. Thus, a main discharge across the main gap occurs substantially instantaneously when the predetermined condition exists.

In one well-known construction, the keep-alive electrode is positioned concentrically within a hollow main electrode, a negative potential of the order of 1000 volts being connected through a resistance of several megohms between the hollow main electrode and the keep-alive electrode. The surrounding main electrode is of relatively small dimensions to give the desired capacity in cooperation with the opposed closely-spaced main electrode, and the concentric electrode is terminated short of this opening in order to confine the ionization to the region near the end of that one main electrode to a desired extent. Such a prior art arrangement with 1000 volts applied between the keep-alive electrode and the main electrode gives some tens or hundreds of microamperes in the glow discharge between the keep-alive and main electrodes, and maintains the number of free electrons in the radio frequency gap between the ends of the hollow main electrode and the opposing main electrode, which may be either solid or hollow.

It has been found difiicult in quantity production to make and position the keep-alive electrode with sufficient accuracy and with adequate clearances to the surrounding electrode to give economic assembly and reasonably long operating life. It is necessary that keep-alive electrode be positioned at a greater distance from the opposing main electrode than from the surrounding main electrode in order to prevent the keep-alive discharge from injecting an excessive number ofelectrons between the hired States Patent ice main electrodes and, in this way, cause unwanted signal VII attenuation. To provide satisfactory operation of the prior art keep-alive structures of the type described, it has been necessary to keep the structure small and mount the keepalive electrode within and in closely spaced relation to the end of the surrounding hollow electrode.

It has been found that during a discharge, transfer of metal, for example by sputtering, from the keep-alive electrode end onto the ends of the main electrode has occurred. This may result in shorting of the keep-alive electrode and one of the main electrodes, or in somecases, shorting of the main electrodes. Also, as a result of this sputtering, the gap capacity, as measured between the main electrodes, and accordingly the tuningof the gap circuit, tends to vary.

The present invention relates to hollow electrodes of the kind adapted to cooperate with an opposing electrode: to form a gap in microwave discharge devices, and particularly to such an electrode including a concentric keep alive electrode.

According to the present invention, the outer hollow electrode of the general type described above is provided with an electrode tip adapted to define with the opposing electrode the discharge gap and extending closer to the gap than the centrally disposed keep-alive electrode, thus permitting the keep-alive electrode to extend longitudinally beyond the body portion of the hollow electrode. This construction allows the use of a larger body portion of the hollow electrode and easier positioning of the keep-alive electrode beyond the end thereof, and at the same time, the gap spacing and the capacity of the gap is determined by the position and dimensions of the electrode tip. The electrode tip is preferably in the form of a relatively open structure having a transverse portion which cooperates with the opposing main electrode since this gives the relatively small area in opposed relation to the other main electrode and leaves an open structure which facilitates the positioning of the keep-alive electrode during manufacture.

The electrode tip, and particularly the transverse section, also act as a shield to protect the narrow gap between the tip and the opposed main electrode from any metal sputtered from the keep-alive electrode. Additional features and advantages of my invention will become more apparent as the following description proceeds, reference being had to the accompanying drawing, and its scope Will be pointed out in the appended claims. In the drawing, Fig. 1 is an elevational view in section of a discharge device having a keep-alive electrode assembly embodying my invention; Fig. 2 is a sectional view along the line 22 of Fig. 1; Fig. 3 is an elevational view, partially in section, showing both opposed electrode structures of similar construction; and Figs. 4-10 inclusive illustrate modifications of electrode structures embodying my invention.

Referring now to Fig. l of the drawing, I have shown my invention embodied in a discharge device including a short section of rectangular wave guide defined by a metallic wall 1, having at the ends thereof, coupling flanges 2 and 3 for coupling at one end with a wave guide extending between a transmitter and an antenna, for example, and at the other end for connection with the receiver. This wave guide section is closed at the ends by window assemblies each including a metallic frame 4 and a dielectric window 5. The windows may to advantage be formed of glass and are suitably dimensioned with respect to the frequency of operation of the system in which the device is to be used.

Extending across the wave guide section 1 intermediate the ends thereof are transverse metal partitions 6 and 7 which are spaced apart, and from the ends of the device in the direction of propagation of waves through.

. 3 the--device;-a distancecorresponding to one-quarter wavelength ah-themperating"frequency?" The partitions, as shown. in Fig. 2, are each provided with a rectangular opening or slot 8 which is centrally locatedwith respect to'-=the cross section'of the; de'vic'er. A*pair-of fconical" 'aresupported" "fronr'the opposite side members 10 andfl walls of the waveguide-in line' with-partition '7." These conical- -members 'provid'era narrow gapj12 at the plane of the partition; A sitrlilarijconicalmember 13 extends upwardly from'the lower'wallfofthet guide at the plane ofpartition 6; and"a 'keep aliv'e' electrode assembly '14 is mountedin the upper wall *of th'e guide and terminates in opposed relation; to the conicalele'ctrode 13;

The electrodegassembly.14 includes a generally cylindric'al"outerelec.trode",.15 jhermeticallyjoinedto the wall oftlfe guide'byjrnea'ns 'of "a suitable'fiange member16 Whiflch"may;be' brazedgto-botlr' the guide and the electrode member -15. A"keep-alive electrode 17in the form of an elongated conductor. is supported inconcentric and insulated relationwithrespecttojthe outer electrode by means, of a glass.gseal ing member318.1 The lower end .of the kep aliye electrodelextendsf below the, lower. end of "the outer electrode- 15,"and iscovered, except at the tip por.tion .or transverseend,.surface,. witha glass. or other. insulating,c0ating..19. A.tip-..portion for the outer electrodetislprovided by a. strap member 20 which, in the particular form,illustrated, ..is in. the form of a U- shaped wire.lobp.,having1the.ends ofthe U brazed or weld'edto -.the'..outer..conductor-.15,.andthe base of the U p0r;tion.,.exte'nding; in. aagenerally paralleland closely spaced 'relatiohwith:respect.to. theopposing electrode 13. As,-illustrated, ;the .opposingamain electrode 13 may be tapered toprovide-a narrow. surfacerin proximity to the wiremember, 20,..and preferably-extending at right angles thereto. In thismanner, it .isupossible to obtain relatively small. BEGQtlVGfgQP varea with relatively rugged electrode construction. Its-will. bo-appreciated "that the electrodes..10. and:11- maywbe .provided. withv narrow portions extending atright'angleszwith respect to one another, ifdesired, in-.,order to provideegap;capacity which is similar to.that..of;the.electrodes13and .14.

The end of the keep-alive electrode-17 is spaced from the .-tip ,20..-by-- an amount-Whichis termed :the. .retraction? The ..retraction.ris fairlygcritical andsvaries with the gas filling compositionand;;.with; thetgelectrode dimensions. Aswaspointed: outrearlier in'zthe specification, it is desired-.to obtain a.,.certa'in .-amount; of .ionization in the vicinityyof; thesgap between-ther main electrodes without having; an. undesirableamount pofsionization between the mainelectrodes underwthosel conditions; when it is desired that the gapibe nonaconducting:v In-aone particular device embodying the present invention; thezmain electrodes and keep-alive electrodes ;wcrer=of:iron or a ferrous alloy and the wire 20w was v of :10205'. diameter nickel. wire. All the metal;parts.xexposedrto.:thexinteriorof the device were electroplated-with:silVer orrcopper; The-retraction exloops 24-ware-mutually: perpendicular providing a small' area-:gap. As; illus trate d,:. the gapl25?btW6Il the spaced portions of the loopst24is slightlylesszthan the retraction 26, between the inner. ;surface,\of the'loops and the ends of, t-he;=l eep.=alive electrodes22.

In.Figs,,.,4 .and, .5,,.. I .haveshown a modified'form of the ,exterior or main.electrodetintheform of a cylinder 27. having an integral.stra zartorming ;the. electrode. tip 7 4. and corresponding generally to the wire loop 24. Figs. 6-10 illustrate modified'formsof the tip'construction which may be used in accordance with my invention. The parts of the electrode structure in general correspond to those of Fig. 3 and corresponding parts andhave been designated by the samereference numerals. In Fig. 6 two U-shaped members 24 have been employed. This construction gives better radio frequency shielding of the tip of the keep-alive electrode. In Fig. 7, a similar construction is used except'that the loop24- is positioned the same as in connection with Fig. 3 and additional wire posts 29 are employedto give the additional shielding. In Fig. 8, the electrodetipis formed by a generally U- shaped wire mesh 30 which isemployed in place of the wire loop 24. In Figs 9 and 10, the tip portion is provided by a plurality of transversely extending wires 31 which are bonded to longitudinally extending portions 32 formed integrally with the outer electrodeZl.

While the wires-illustrated 'have'been of circular cross. section; wires :or straps or non-circular cross section may be used and local sharpportions or edges may be em-Z ployed .toincrease 'th'elra'dio frequency field 'strengthiiof particular parts of'the gap between the electrodetips, if desired.

While :I "have'shown and described particular embodi ments' of my invention, it will'be. apparent to those skilled in the arcthat-changes and modifications maybe.

made without departing from my invention in its better aspect and aim therefore in the appended claims to cover allsuch changesand modifications-as fall within the true.

spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent oftth'e United States is:

1. A high frequency electric discharge device comprising a main electrode and a concentric-type electrodestructure mounted in endwise spaced and opposed relation withirespect thereto to define a discharge gap,.

said'concentric-type electrode structure comprising an outer member having a longitudinalpassage therethr'ough, a keep-alive electrode. supported within said passage. in

insulatedfrela'tion to said outer member and havingthe end thereof extending beyond the end of saidouter member toward said. main electrode, said.outer memberineluding a member small in' cross. section in comparison withsa'id.outermember extending from the outer. surface.

of said outer member longitudinally-beyond said, keep-.

alive electrode and 'having a portion spaced from the end of said main electrode forming said discharge. gap.

2." A "high 'frequencyelectric discharge device compris inga mainelectrode and a concentric electrode structure mounted in. opposed endwise and spaced relation with respect thereto', said concentric electrode structure. comprising an outer conducting-member having a longitudinal sidehwalls .ofvsaid conducting member with thebase of the U-shaped conductor extending r transversely across thepassage in said conducting member and cooperating; withthegendof. said main'electrode formingsaidydis? charge @gap.

3.-Aihigh;i.-frequency electric". discharge deviceuin eludinga main electrode? and a concentric-type electrode supported in opposed endwise and spaced relationwwitlrrespect thereto to provide a discharge gap, said concentrictype:electrode-;comprisingr.an outer conducting member havingga :longitudinalpassage :extending .therethrough, a keepi-aliveelectrodeincluding a portion supported in said passagein concentric relation. with respect to said conduct-= ing-member and. extending longitudinally beyond the endof said conducting member; said portion or said keep-alive electrode-including ;a transverse: end 'surface and-being I completely floated withean insulating material except for.

said transverse end surface, and a conductive element of small cross section in comparison with said conducting member extending longitudinally from the side wall of said conducting member toward said main electrode and cooperating with said oppositely mounted main electrode [forming said discharge gap.

4. The device as defined in claim 3 wherein said conductive element is 'U-shaped and is integral with said conducting member.

5. An electrode structure for use in a high frequency electric discharge device comprising an outer conducting member having a longitudinal passage extending therethrough, a keep-alive electrode supported in said passage in insulated relation with respect to said conducting member and extending longitudinally beyond the end of said member and a generally U-shaped conductor joined to the side walls of said conducting member with the base of the U-shaped member extending transversely across the passage in said conducting member, .a second electrode oppositely mounted with respect to said electrode structure and having an elongated transverse surface extending substantially perpendicular to the transverse portion of said U-shaped member and forming therewith a gap.

6. An electrode structure for use in a high frequency electric discharge device comprising an outer conducting member having a longitudinal passage extending therethrough, a keep-alive electrode including a transverse end surface and being supported in said passage in said conducting member with said transverse end surface extending longitudinally beyond the end of said member, said keep-alive electrode being completely coated with an insulating material except for said transverse end surface, a generally U-shaped conductive structure including a plurality of conductors joined to the side walls of said conducting member with the base of the U-shaped structure comprising a plurality of individual conductive elements extending transversely across the passage in said conducting member, and a second electrode oppositely mounted with respect to said U-shaped structure for cooperation with said plurality of individual conductive elements and forming a discharge gap therewith.

7. An electrode structure for use in a high frequency discharge device, comprising an outer conducting member having a longitudinal passage extending therethrough, a keep-alive electrode supported in said passage in insulated relation with respect to said conducting member, a generally U-shaped conductor joined to the side walls of said conducting member with the base of the U-shaped conductor extending transversely across the passage in said conducting member, and a second electrode oppositely mounted with respect to said electrode structure and having a generally U-shaped conductor disposed substan- 8. An electrode structure for use in a high frequency discharge device, comprising an outer conducting member having a longitudinal passage extending therethrough, a keep-alive electrode insulatingly supported in said passage, a pair of generally U-shaped conductors projecting from the side wallsof said conducting member with the bases of the U-shaped member extending in substantially mutual parallel relation and in diametrally opposed relation across the passage in said conducting member, and a second electrode oppositely mounted with respect to said conducting member and having an elongated transverse surface spaced from said U-shaped conductors and forming therewith a gap.

9. An electrode structure for use in a high frequency discharge device, comprising an outer conducting member having a longitudinal passage extending therethrough, a keep-alive electrode supported in said passage in insulated relation with respect to said conducting member, a generally U-shaped wire mesh joined to the side walls of said conducting member with the base of the mesh extending transversely across the passage in said conducting member, and a second electrode oppositely mounted with respect to said conducting member and forming with said mesh a gap.

10. An electrode structure for use in a high frequency discharge device, comprising an outer conducting member having a longitudinal passage extending therethrough, an auxiliary electrode insulatingly supported in said passage, a generally U-shaped conductor joined to the side walls of said conducting member with the base of the U-shaped conductor extending transversely across the passage in said conducting member, a pair of conductive rod members joined to the side walls of said conducting member and arranged in space quadrature with respect to said U-shaped conductor, and a second electrode oppositely mounted with respect to said electrode member and having an elongated transverse surface extending substantially perpendicular to the transverse portion of said U-shaped conductor and forming therewith a gap.

References Cited in the file of this patent UNITED STATES PATENTS 1,941,279 Sharpnack Dec. 26, 1933 2,081,500 Nowosielski May 25, 1937 2,280,962 McDougal Apr. 28, 1942 2,415,962 Okress Feb. 18, 1947 2,427,089 Clifiord Sept. 9, 1947 2,442,945 Andersen June 8, 1948 2,454,761 Barrow et al Nov. 30, 1948 2,494,570 Mezger I an. 17, 1950 

